Experimental Foot-and-mouth disease virus (FMDV) infection induces reversible exocrine pancreatic insufficiency and irreversible endocrine pancreatic insufficiency in Holstein-Friesian crossbred heifers

As hyperglycemia is a consistent finding in cattle recovered from FMD, we hypothesized that damage to the pancreas by FMD virus (FMDV) is the basis for the alterations in energy metabolism. Accordingly, crossbred heifers were either inoculated with virulent FMDV serotype O by intradermolingual (n = 7) or mock-infected with saline (n = 7). Blood samples were collected on day 0, 7, 14, 30, 60, 90, 120, 150, and 180 post-infection (dpi) to determine the concentrations of exocrine pancreatic enzymes, insulin, and indicators of energy metabolism. The results indicated a significant elevation in the serum amylase, lipase, and TLI by dpi 7 in FMDV-infected heifers that returned to baseline by dpi 60–120. In contrast, decrease in the serum insulin, first recorded on dpi 14, persisted till dpi 180 (P < 0.0001). The circulating concentrations of glucose, glycated hemoglobin, triglycerides, NEFA and BHB showed a significant increase by dpi 30 and did not recede to basal level till dpi 180 in the FMDV-infected group (P < 0.0001). Pancreatic histopathology and immunohistochemistry in a heifer that died on 12 dpi revealed necrotic and inflammatory changes in the pancreas with intense immunolabeling for FMDV antigens both in the pancreatic acini and islets. In another heifer that died on dpi 49, regenerative changes were found in the exocrine pancreas, while necrotic changes persisted in the islets of Langerhans, with moderate FMDV antigen labeling. It was concluded that experimental FMDV infection-induced endocrine pancreatic insufficiency was irreversible, whereas exocrine pancreatic function could be restored by dpi 120.